U.S. patent number 5,531,111 [Application Number 08/431,043] was granted by the patent office on 1996-07-02 for structure of a volumetric measuring apparatus.
This patent grant is currently assigned to Nippondenso Co., Ltd.. Invention is credited to Yasuhiro Horiuchi, Yoshiyuki Okamoto, Hidekuni Sugi, Kouichi Yamada, Kazuhiko Yamaguchi.
United States Patent |
5,531,111 |
Okamoto , et al. |
July 2, 1996 |
Structure of a volumetric measuring apparatus
Abstract
A volumetric measurement apparatus is provided which measures
the volume of a liquid material stored within a container. The
volumetric measurement apparatus includes a reference enclosure
having disposed therein a single pressure sensor. The pressure
sensor has a pressure sensitive element exposed to both internal
spaces of the reference enclosure and the container to detect a
pressure difference between the container and the reference
enclosure. A sensor shielding member is arranged in the reference
enclosure to selectively shield the pressure sensitive element from
the internal space of the reference enclosure to detect only a
pressure within the container. The volumetric measurement is made
based on the pressure difference between the container and the
reference enclosure and the pressure in the container.
Inventors: |
Okamoto; Yoshiyuki (Nagoya,
JP), Horiuchi; Yasuhiro (Toyota, JP),
Yamada; Kouichi (Aichi, JP), Yamaguchi; Kazuhiko
(Gifu, JP), Sugi; Hidekuni (Nagoya, JP) |
Assignee: |
Nippondenso Co., Ltd.
(Aichi-Pref., JP)
|
Family
ID: |
26360558 |
Appl.
No.: |
08/431,043 |
Filed: |
April 28, 1995 |
Foreign Application Priority Data
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Apr 28, 1994 [JP] |
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6-092687 |
Feb 10, 1995 [JP] |
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7-023237 |
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Current U.S.
Class: |
73/149;
73/290V |
Current CPC
Class: |
B60K
15/061 (20130101); G01F 17/00 (20130101); G01F
23/14 (20130101) |
Current International
Class: |
B60K
15/06 (20060101); B60K 15/03 (20060101); G01F
23/14 (20060101); G01F 17/00 (20060101); G01F
017/00 () |
Field of
Search: |
;73/149,29V,861.47 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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486264A2 |
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May 1992 |
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EP |
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59-164916 |
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Sep 1984 |
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JP |
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2-19716 |
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Jan 1990 |
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JP |
|
0200019 |
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Sep 1991 |
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JP |
|
4-47231 |
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Feb 1992 |
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JP |
|
4268416 |
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Sep 1992 |
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JP |
|
620977 |
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Jun 1994 |
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JP |
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6273212 |
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Sep 1994 |
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JP |
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Primary Examiner: Chilcot; Richard
Assistant Examiner: Amrozowicz; Paul D.
Attorney, Agent or Firm: Cushman Darby & Cushman
Claims
What is claimed:
1. A volumetric measuring apparatus for measuring the volume of a
given material stored within a container comprising:
a reference enclosure, disposed within the container, defining
therein a reference cavity having a preselected volume;
pressure balancing means for balancing static pressures in the
container and said reference enclosure with each other;
pressure difference producing means for producing a pressure
difference between pressures in the container and said
enclosure;
a pressure sensor having a pressure sensitive element exposed
inside both the container and said reference enclosure, said
pressure sensitive element being sensitive to a pressure acting
thereon to provide a sensor signal indicative thereof;
sensor mode switching means for switching an operation of said
pressure sensor between a first operation mode and a second
operation mode, the first operation mode being such that the
pressure sensitive element of said pressure sensor is sensitive to
said pressure difference between the container and said reference
enclosure, the second operation mode being such that the pressure
sensitive element of said pressure sensor is sensitive to a
pressure only in one of the container and said reference
enclosure;
control means for controlling operations of said pressure
difference, producing means and said sensor mode switching means in
first and second control modes, the first control mode being such
that said pressure difference producing means produces said
pressure difference between the container and said reference
enclosure and said sensor mode switching means activates said
pressure sensor in the first operation mode to provide a first
sensor signal indicative of said pressure difference, the second
control means being such that said pressure difference producing
means produces said pressure difference and said sensor mode
switching means activates said pressure sensor in the second
operation mode to provide a second sensor signal indicative of the
pressure in the one of the container and said reference enclosure;
and
volume determining means for determining the volume of the given
material stored within the container based on the first sensor
signal and the second sensor signal provided by said pressure
sensor.
2. A volumetric measuring apparatus as set forth in claim 1,
wherein said volume determining means determines the volume of said
given material based on a ratio of outputs values of the first and
second sensor signals.
3. A volumetric measuring apparatus as set forth in claim 1,
wherein said sensor mode switching means includes a cover member
formed to define therein a preselected volume and opening and
closing means, said cover member having disposed therein the
pressure sensitive element of said pressure sensor, said opening
and closing means selectively opening and closing said cover member
to establish the first and second operating modes of said pressure
sensor.
4. A volumetric measuring apparatus as set forth in claim 3,
wherein the preselected volume in said cover member is so defined
as to compensate for an error in determining the volume of the
given material within the container caused by a variation in
internal static pressure of the container.
5. A volumetric measuring apparatus as set forth in claim 4,
wherein said volume determining means determines the volume Vf of
the given material stored within the container according to the
following equation:
where Va is a volume in the container, Vc is a, volume in said
reference enclosure, Pc is a pressure change in said reference
enclosure, and Pt is a pressure change in the container.
6. A volumetric measuring apparatus as set forth in claim 3, said
cover member has a communication port which establishes
communication between the pressure sensitive element of said
pressure sensor and an internal space of the one of the container
and said reference enclosure, said opening and closing means being
responsive to a control signal from said control means to
selectively establish and block said communication to have said
pressure sensor assume the first and second operation modes.
7. A volumetric measuring apparatus as set forth in claim 1,
wherein said pressure difference producing means is disposed within
said reference enclosure and generates a vibration within the
container to change a volume in the container, and wherein said
pressure sensor detects a pressure change in the container in the
second operation mode.
8. A volumetric measuring apparatus as set forth in claim 7,
wherein said pressure difference producing means is provided with
an acoustic speaker which has a diaphragm oriented toward a bottom
of the container and which transmits a preselected frequency of
vibration inside the container through a propagation hole formed in
the bottom of the container to produce a pressure variation in the
container.
9. A volumetric measuring apparatus as set forth in claim 7,
wherein said reference enclosure includes a first chamber and a
second chamber, said second chamber being disposed on an outer
bottom wall of said first chamber and communicating with the first
chamber and an internal space of the container through a first
opening and a second opening, respectively, and further comprising
a float member having a specific gravity smaller than that of the
given material to block the second opening when the given material
reaches a given level within the container.
10. A volumetric measuring apparatus as set forth in claim 8,
wherein the given material stored within the container is liquid,
and further comprising capillary means for attracting and directing
a portion of liquid collected on the bottom of said reference
enclosure to a heating element of the speaker for evaporation.
11. A volumetric measuring apparatus as set forth in claim 1,
wherein said reference enclosure includes an inner housing disposed
within the container and an outer housing, disposed out of the
container, communicating with the inner housing.
12. A volumetric measuring apparatus as set forth in claim 11,
wherein said pressure difference producing means, said pressure
sensor, and said sensor mode switching means are arranged within
the inner housing.
13. A volumetric measuring apparatus as set forth in claim 11,
wherein said inner housing of said reference enclosure communicates
with said outer housing through an opening formed in the container,
said outer housing having a through hole into which a bolt is
inserted to secure the outer housing on an outer upper surface of
the container.
14. A volumetric measuring apparatus as set forth in claim 1,
wherein said reference enclosure has an opening formed in a bottom
wall thereof to return a portion of the given material collected on
the bottom back into the container.
15. A volumetric measuring apparatus as set forth in claim 1,
wherein the pressure sensitive element of said pressure sensor has
a surface oriented vertically of said reference enclosure.
16. A volumetric measuring apparatus as set forth in claim 15,
wherein said reference enclosure is made of a cylindrical member
which has a flat surface formed on a side wall for mounting a
volumetric measuring assembly composed of said pressure sensor and
said sensor mode switching means.
17. A volumetric measuring apparatus as set forth in claim 7,
wherein said reference enclosure has a hollow extension, extending
outwardly from a bottom thereof, communicating with an internal
space of the container, said hollow extension forming a confined
space, defined by a surface of the given material when blocking the
communication with the internal space of the container and said
pressure difference producing means disposed within said reference
enclosure to decrease an internal pressure of said reference
enclosure indicated by said pressure sensor below a given threshold
value, said volumetric determining means determining that the
container is filled with the given material when said internal
pressure indicated by said pressure sensor is smaller than said
given threshold value.
18. A volumetric measuring apparatus as set forth in claim 17,
wherein said hollow extension having a length L which is so
determined as to satisfy the following relation:
where a is a change in level of the given material caused by a
maximum inclination thereof within the container, b is a change in
level of the given material caused by vibrations of the surface of
the given material, and x is given by the relation of
x=.rho..multidot.g.multidot.h.multidot.Vc/S where g is an
acceleration acting on the given material, S is a sectional area of
said hollow extension, h is a height between a preselected maximum
level of the given material within the container and an lower end
of said hollow extension, .rho. is a specific gravity of the given
material, and Vc is the given volume of said reference
enclosure.
19. A volumetric measuring apparatus as set forth in claim 17,
wherein said hollow extension is designed to have a resonance
frequency co which is different from a vibration frequency of said
pressure difference producing means and which is determined by the
following relation: ##EQU5## where m is a mass of the given
material, ksr is air spring constant of said confined space of said
hollow extension, and ksp is a mechanical spring constant of a
vibration producing means of said pressure difference producing
means.
20. A volumetric measuring apparatus as set forth in claim 1,
wherein said control means includes a circuit board, said pressure
sensor and said sensor mode switching means being incorporated
within a volumetric measuring assembly which is disposed within
said reference enclosure, said circuit board being mounted over the
volumetric measuring assembly.
21. A volumetric measuring apparatus as set forth in claim 20,
wherein said reference enclosure has an opening enclosed by a
flange member which is mounted on an upper outer surface of the
container, said circuit board being secured on said flange
member.
22. A volumetric measuring apparatus as set forth in claim 6,
wherein said opening and closing means includes a casing having a
wall and a movable member movable into engagement with the wall of
the casing to establish the communication between the pressure
sensitive element of said pressure sensor and the internal space of
the one of the container and said reference enclosure, said movable
member having a tapered end portion, the wall of said casing having
a tapered bulge portion for receiving therein the tapered end
portion of said movable member when said communication is
established.
23. A volumetric measuring apparatus as set forth in claim 7,
wherein said control means includes a phase detector which extracts
an output signal component outputted by said pressure sensor having
a frequency produced for operating said pressure difference
producing means, and which outputs the extracted signal component
to said volume measuring means.
24. A volumetric measuring apparatus as set forth in claim 7,
wherein said control means includes a phase detector which combines
the sensor signal from said pressure sensor and a signal
synchronizing with a frequency of the vibration produced by said
pressure difference producing means to provide a DC signal to said
volume determining means.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates generally to a volumetric measuring
apparatus, and more particularly to an improved structure of a
volumetric measuring apparatus which measures the volume of a
liquid material stored within a container by subtracting the volume
of gas filling an empty portion of the container from the volume of
the container.
2. Background Art
Japanese Patent First Publication No. 59-164916 teaches a
volumetric measurement system which has a pair of volume-changing
means and a pressure sensor means. The volume-changing means are
disposed within a liquid-stored container and a reference enclosure
communicating with the container. The pressure sensor means detects
pressures in the container and the reference enclosure
independently. The volume of the liquid in the container is
determined based on a ratio of the pressures in the container and
the reference enclosure.
In order to detect the pressures in the container and the reference
enclosure, the above prior art volumetric measurement system
teaches two pressure sensors mounted in the container and the
reference enclosure, respectively. As an alternative form, a single
pressure sensor and a directional control valve are also proposed.
In this arrangement, the pressure sensor communicates with the
container and the reference enclosure through separate pressure
lines. The directional control valve switches between the pressure
lines to detect the pressures in the container and the reference
enclosure separately. These prior art arrangements, however, result
in a complex structure of the volumetric measurement system,
increasing manufacturing costs.
SUMMARY OF THE INVENTION
It is, therefore, a principal object of the present invention to
avoid the disadvantages of the prior art.
It is another object of the present invention to provide an
improved simple structure of a volumetric measuring apparatus which
includes a single pressure sensor means designed to detect
pressures both in a container and a reference enclosure.
According to one aspect of the present invention, there is provided
a volumetric measuring apparatus for measuring the volume of a
given material stored within a container which comprises (a) a
reference enclosure, disposed within the container, defining
therein a reference cavity having a preselected volume, (b) a
pressure balancing means for balancing static pressures in the
container and the reference enclosure with each other, (c) a
pressure difference producing means for producing a pressure
difference between pressures in the container and the enclosure,
(d) a pressure sensor having a pressure sensitive element exposed
inside both the container and the reference enclosure, the pressure
sensitive element being sensitive to a pressure acting thereon to
provide a sensor signal indicative thereof, (e) a sensor mode
switching means for switching an operation of the pressure sensor
between a first operation mode and a second operation mode, the
first operation mode being such that the pressure sensitive element
of the pressure sensor is sensitive to the pressure difference
between the container and the reference enclosure, the second
operation mode being such that the pressure sensitive element of
the pressure sensor is sensitive to a pressure only In one of the
container and the reference enclosure, (f) a control means for
controlling operations of the pressure difference producing means
and the sensor mode switching means in first and second control
modes, the first control mode being such that the pressure
difference producing means produces thee pressure difference
between the container and the reference enclosure and the sensor
mode switching means activates the pressure sensor in the first
operation mode to provide a first sensor signal indicative of the
pressure difference, the second control means being such that the
pressure difference producing means produces the pressure
difference and the sensor mode switching means,activates the
pressure sensor in the second operation mode to provide a second
sensor signal indicative of the pressure in the one of the
container mad the reference enclosure, and (g) a volume determining
means for determining the volume of the given material stored
within the container based on the first sensor signal and the
second sensor signal provided by the pressure sensor.
In the preferred mode of the invention, the volume determining
means determines the volume of the given material based on a ratio
of outputs values of the first and second sensor signals.
The sensor mode switching means includes a cover member formed to
define therein a preselected volume and an opening and closing
means. The cover member has disposed therein the pressure sensitive
element of the pressure sensor. The opening and closing means
selectively opens and closes the cover member to establish the
first and second operating modes of the pressure sensor.
The preselected volume in the cover member is so defined as to
compensate for an error in determining the volume of the given
material within the container caused by a variation in internal
static pressure of the container.
The cover member has a communication port which establishes
communication between the pressure sensitive element of the
pressure sensor and an internal space of the one of the container
and the reference enclosure. The opening and closing means is
responsive to a control signal from the control means to
selectively establish and block the communication to have the
pressure sensor assume the first and second operation modes.
The pressure difference producing means is disposed within the
reference enclosure and generates a vibration within the container
to change a volume in the container. The pressure sensor detects a
pressure change in the container in the second operation mode.
The pressure difference producing means is provided with an
acoustic speaker which has a diaphragm oriented toward a bottom of
the container and which transmits a preselected frequency of
vibration inside the container through a propagation hole formed in
the bottom of the container to produce a pressure variation in the
container.
The reference enclosure may include a first chamber and a second
chamber. The second chamber is disposed on an outer bottom wall of
the first chamber and communicating with the first chamber and an
Internal space of the container through a first opening and a
second opening, respectively. A float member is further provided
which has a specific gravity smaller than that of the given
material to block the second opening when the given material
reaches a given level within the container.
The given material stored within the container is liquid. A
capillary means may be further provided for attracting and
directing a portion of liquid collected on the bottom of the
reference enclosure to a heating element of the speaker for
evaporation.
The reference enclosure may includes an inner housing disposed
within the container and an outer housing, disposed out of the
container, communicating with the Inner housing. The pressure
difference producing means, the pressure sensor, and the sensor
mode switching means may be arranged within the inner housing. The
inner housing of the reference enclosure communicates with the
outer housing through an opening formed in the container. The outer
housing has a through hole into which a bolt is inserted to secure
the outer housing on an outer upper surface of the container.
The reference enclosure may have an opening formed in a bottom wall
thereof to return a portion of the given material collected on the
bottom back into the container.
The pressure sensitive element of the pressure sensor has a surface
oriented vertically of the reference enclosure.
The reference enclosure is made of a cylindrical member which has a
flat surface formed on a side wall for mounting a volumetric
measuring assembly composed of the pressure sensor and the sensor
mode switching means.
The reference enclosure may have a hollow extension, extending
outwardly from a bottom thereof, communicating with the internal
space of the container. The hollow extension forms a confined space
defined by a surface of the given material when blocking the
communication with the internal space of the container and the
pressure difference producing means disposed within the reference
enclosure to decrease an internal pressure of the reference
enclosure indicated by the pressure, sensor below a given threshold
value. The volumetric determining means determines that the
container is filled with the given material when the internal
pressure indicated by the pressure sensor is smaller than the given
threshold value.
The control means includes a circuit board. The pressure sensor and
the sensor mode switching means may be incorporated within the
volumetric measuring assembly which is disposed within the
reference enclosure. The circuit board may be mounted over the
volumetric measuring assembly.
The reference enclosure may have an opening enclosed by a flange
member which is mounted on an upper outer surface of the container.
The circuit board is secured on the flange member.
The opening and closing means includes a casing having a wall and a
movable member movable into engagement with the wall of the casing
to establish the communication between the pressure sensitive
element of the pressure sensor and the internal space of the one of
the container and the reference enclosure. The movable member may
have a tapered end portion. The wall of the casing may have a
tapered bulge portion for receiving therein the tapered end portion
of the movable member when the communication is established between
the pressure sensitive element and the internal space of the one of
the container and the reference enclosure.
The control means includes a phase detector which extracts an
output signal component outputted by the pressure sensor having a
frequency produced for operating the pressure difference producing
means, and which outputs the extracted signal component to the
volume determining means.
The phase detector may combine the sensor signal from the pressure
sensor and a signal synchronizing with a frequency of the vibration
produced by the pressure difference producing means to provide a DC
signal to the volume determining means.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood more fully from the
detailed description given hereinbelow and from the accompanying
drawings of the preferred embodiment of the invention, which,
however, should not be taken to limit the invention to the specific
embodiment but are for explanation and understanding only.
In the drawings:
FIG. 1 is a cross sectional view which shows a volumetric measuring
apparatus according to the present invention;
FIG. 2 is a cross sectional view which shows a modification of the
volumetric measuring apparatus shown in FIG. 1;
FIG. 3 is a schematic view which shows a volumetric measuring
assembly;
FIG. 4 is a cross sectional view which shows the volumetric
measuring assembly shown in FIG. 3;
FIG. 5 is a circuit diagram of a control unit of a volumetric
measuring apparatus;
FIG. 6 is a cross sectional view which shows a container partly
deformed by a variation in internal pressure;
FIG. 7 is a graph which shows a relation between a measured volume
of fuel stored within a fuel tank and the amount of the fuel within
the fuel tank;
FIG. 8 is a cross sectional view which shows a volumetric measuring
assembly;
FIG. 9 is a graph which shows relations between the volume of a
back chamber of an opening and closing unit and a variation in
sensor output caused by a change in atmospheric pressure;
FIG. 10 is a graph which shows a volume measurement error caused by
a variation in atmospheric pressure;
FIG. 11 is a cross sectional view which shows a volumetric
measuring apparatus according to a third embodiment of the
invention;
FIG. 12 is a cross sectional view which shows a volumetric
measuring apparatus according to a fourth embodiment of the
invention;
FIG, 13 is a cross sectional view which shows an opening and
closing unit of a volumetric measuring assembly according to a
fifth embodiment of the invention,
FIGS. 14 and 15 are cross sectional views which show a reference
enclosure according to a sixth embodiment of the invention;
FIG. 16 is a graph which shows a variation in pressure monitored by
a pressure sensor caused by a change in surface of a liquid
material stored in a fuel tank;
FIG. 17 is a cross sectional view which shows a modification of a
volumetric measuring apparatus;
FIG. 18 is a cross sectional view which shows a volumetric
measuring apparatus according to a seventh embodiment of the
invention;
FIG. 19 is a traverse sectional view taken along the line I--I in
FIG. 18;
FIG. 20 is a cross sectional view which shows an opening and
closing unit of a volumetric measuring assembly according to an
eighth embodiment of the invention;
FIG. 21 a graph which shows a relation between an attraction acting
on an armature of a solenoid valve of an opening and closing unit
and a distance between the armature and a wall of a casing;
FIG. 22 is a circuit diagram which shows a control unit according
to a ninth embodiment of the invention;
FIG. 23 is a circuit diagram which shows a phase detector of the
control unit shown in FIG. 22; and
FIGS. 24(a) to 24(d) are time charts which show waveforms of
signals inputted to and outputted from the phase detector shown in
FIG. 23.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, wherein like numbers refer to like
parts in several views, particularly to FIG. 1, there is shown a
volumetric measuring apparatus i according to the present
invention.
The volumetric measuring apparatus i includes a reference enclosure
3 within a fuel tank 2 which defines therein a reference cavity in
which an acoustic speaker 4 and a volumetric measuring assembly 8
are disposed.
The volumetric measuring apparatus 1 further includes a control
unit 14, as shown in FIG. 5, which is mounted outside the fuel tank
2. The control unit 14 is composed of a speaker driver 11 for
driving the speaker 4, an opening and closing unit controller 12
for controlling an operation of the opening and closing unit 7, and
a volumetric measuring circuitry 13 which is responsive to a signal
from the pressure sensor 5 to determine the volumes of gas and fuel
within the fuel tank 2. The speaker 4, the speaker driver 11, the
opening and closing unit 7, and the opening and closing unit
controller 12, the pressure sensor 5, and,the volumetric measuring
circuitry 13 are, as can be seen in FIG. 1, Connected through lead
wires 15 and a connector 16.
The reference enclosure 3 is formed with a vertically extending
cylindrical member having a fixed volume which includes an inner
housing 21 disposed within the fuel tank 2 and an outer housing 22,
communicating with the inner housing 21, arranged on an upper
surface of the fuel tank 2. The fuel tank 2 has a circular opening
23 through which the inner housing 21 of the reference enclosure 3
is inserted. Disposed around the circular opening 23 is a tank
flange 24 which secures the reference enclosure 3 and seals the
circular opening 23. The tank flange 24 has therearound a plurality
of nuts fixed by welding, for example.
The outer housing 22 is greater in diameter than the tank opening
23, and has a plurality of vertically extending bolt holes 27
through which bolts 26 are inserted for engagement with the nuts 25
to mount the reference enclosure 3 on the fuel tank 2.
Note that the volume of the reference enclosure 3 may be changed
easily by using a vertically extending outer housing 22, as shown
in FIG. 2, instead of the one shown in FIG. 1.
The speaker 4 is oriented downward and mounted on a fiat bottom
surface of the inner housing 21 using screws. The bottom surface of
the inner housing 21 has formed therein a plurality of propagation
openings 28 each having a diameter of more than 5 mm for
propagating pressure variations produced by vibrations of a cone
sheet (i.e., a diaphragm) of the speaker 4 into the fuel tank
2.
In a portion of the bottom of the inner housing 21 around the
speaker 4, at least one leakage hole 29 is formed which establishes
communication between the reference enclosure 3 and the fuel tank
2. The leakage hole 29 serves to return a liquid fuel collected on
the bottom of the inner housing 21 back to the fuel tank 2 and
balances a static pressure within the fuel tank 2 with that within
the reference enclosure 3. The diameter of the leakage hole 29 is
so set as to restrict transmission of an output from the speaker 4
which has, for example, an inaudible frequency of 10 to 40 Hz.
The volumetric measuring assembly 8, as shown in FIGS. 3 and 4,
includes a pressure sensor 5, a back chamber housing 6, and, an
opening and closing unit 7. The back chamber housing 6 defines
therein a back chamber 70, and has formed therein a communication
port 31 for communication with the inside of the reference
enclosure 3. The opening and closing unit 7 is operable to
selectively open and close the communication port 31. The pressure
sensor 5 has a vibratory plate or diaphragm 32 which vertically
extends and isolates the back chamber from the fuel tank 2. The
pressure sensor 5 senses vibrations of the diaphragm 32 and
converts them into electric signals.
The back chamber 70 has a preselected volume which is, as will be
discussed later in detail, so defined by the inner wall thereof and
the diaphragm 32 as to substantially eliminate a measurement error
caused by a variation in internal pressure of the fuel tank 2 and a
variation in atmospheric pressure surrounding the fuel tank 2.
The pressure sensor 5 also includes a piezoelectric element 33
attached to almost the entire surface of the diaphragm 32. The
diaphragm 32 is responsive to the pressure acting thereon to
deform. The piezoelectric element 33 converts the mechanical
deformation of the diaphragm 32 into an electric energy to produce
a voltage to the volumetric measuring circuitry 13 of the control
unit 14. Note that the pressure sensor 5 may alternatively be
provided with any other sensor such as a microphone or a speaker
which is capable of translating a pressure variation into an
electric signal.
The opening and closing unit 7 is, as shown in FIG. 4, provided
with a solenoid valve. When a solenoid 34 is energized in response
to a control signal from the opening and closing unit controller 12
of the control unit 14, it will produce an electromagnetic force to
draw an armature 35 against a spring force of a spring 36, so that
the communication port 31 is opened, while when the solenoid 34 is
deenergized, the armature 35 is urged by the spring force of the
spring 36 so as to close the communication part 31. Installed on an
end portion of the armature 35 is a rubber packing or seal 37 for
hermetically sealing the communication port 31 when closed by the
armature 35. Openings 38 are formed in a valve casing for
communication between the communication port 31 and the reference
enclosure 3.
The openings 38 may be placed with a single hole. Additionally, the
solenoid valve may be placed by an electric motor or a bimetal.
The volumetric measuring assembly 8 is retained by screws on a
mounting portion 39 formed on an inner side wall of the inner
housing 21 so as to orient the diaphragm 32 of the pressure sensor
5 vertically. The mounting portion 39 has a flat surface for
facilitating easy installation of the volumetric measuring assembly
8.
The control unit 14, as already discussed, includes the speaker
driver 11, the opening and closing unit controller 12, and the
volumetric measuring circuitry 13. The speaker driver 11, as shown
in FIG. 5, includes an oscillator 41 producing a wave signal having
a given frequency (e.g., 10 to 40 Hz) and a power amplifier 42
amplifying the wave signal produced by the oscillator 41 to
transmit it to the speaker 4.
The volumetric measuring circuitry 13 includes a preamplifier 43, a
band-pass filter 44, a phase detector 45, a CPU 46, and a display
47. The preamplifier 43 amplifies an output from the pressure
sensor 5 to provide it to the band-pass filter 44. The band-pass
filter 44 attenuates frequencies other than the frequency produced
by the oscillator 41 to remove unwanted noise from the output of
the preamplifier 43. The phase detector 45 extracts an output
signal component having the frequency produced by the oscillator
41. The CPU 46 determines the volume of liquid fuel stored in the
fuel tank 2 and the volume of gas filling an empty portion of the
fuel tank 2 based on the output from the phase detector 45. The
display 47 may be installed in a cabin of an automotive vehicle to
inform an vehicle operator of the volume of the liquid fuel
remaining in the fuel tank 2 determined by the CPU 46.
The opening and closing unit controller 12 has a switch 48 which
turns on and off in response to a command from the CPU 46 to
control energization of the solenoid 34 of the opening and closing
unit 7.
A basic operation of the CPU 46 to determine the volume of fuel in
the fuel tank 2 will be discussed below.
When the communication port 31 of the pressure sensor 5 is opened
by the opening and closing unit 7, the pressure sensor 5 detects a
pressure difference or variation .DELTA.P, if produced, between a
pressure change Pc in the reference enclosure 3 and a pressure
change Pt in the fuel tank 2 (.DELTA.P=Pc-Pt). Conversely, when the
communication port 31 is closed, the pressure sensor 5 detects only
the pressure change Pt in the fuel tank 2.
The CPU 46 determines a volume of gas vt within the fuel tank 2
according to the following equation:
where Vc is the volume of the reference enclosure 3.
If the volume of the fuel tank 2 is defined as Va, a volume of the
fuel Vf may be expressed by the following relation:
The CPU 46 determines the volume of fuel Vf within the fuel tank 2
based on the following equation which is obtained by both the above
equations (1) and (2).
Next, an operation of the CPU 46 using the speaker 4 to improve the
accuracy of volumetric measurement will be discussed below.
When the speaker 4 is actuated, it will cause the corn sheet
thereof (i.e, the diaphragm) to vibrate, leading to a variation in
volume .DELTA.V so that the pressure change Pt in the fuel tank 2
is caused. The pressure change Pc in the reference enclosure 3
under this condition may be given by the following equation:
where .gamma. is a ratio of specific heat and Po is a static
pressure.
The fuel tank 2, when the speaker is actuated to cause the pressure
change Pt in the fuel tank 2, deforms mechanically as shown in FIG.
6. The mount of the mechanical deformation .DELTA.Va may be
expressed by the following equation:
where kt is a deformation factor dependent upon the rigidity of the
fuel tank 2.
Thus, the pressure change Pt in the fuel tank 2 when the speaker 4
is operated to produce the volume variation .DELTA.V may be given
by the following relation:
Accordingly, the volume of fuel Vf within the fuel tank 2 may be
derived by the following relation:
The term (.gamma..multidot.Po.multidot.kt.multidot.Va) in the above
equation is an offset term. The static pressure Po is dependent
upon a variation in static pressure difference between internal
pressure of the fuel tank 2 and atmospheric pressure caused by a
variation in amount of fuel vapor (e.g., gasoline vapor) and a
variation in atmospheric pressure. Usually, the static pressure
difference varies over a range from -5 kPa activating a filler cap
relief valve to 20 kPa activating a canister check valve. The
atmospheric pressure also varies over a range from 100 kPa at an
altitude of zero (0) to, for example, 60 kPa at the top of Mt.
pikes having an altitude of 4300 m in Colorado of the U.S. Note
that 55 kPa<Po<120 kPa.
As will be appreciated from the above, under the variation in the
static pressure Po, a difference will occur, as shown in FIG. 7,
between an actual volume of fuel (indicated by a broken line) and
the volume of fuel Vf (indicated by a solid line) derived by the
equation (1).
An output voltage ec of the pressure sensor 5 when the
communication port 31 is opened may be given by the following
equation:
where b is a sensor sensitivity (V/Pa).
An output voltage et of the pressure sensor 5 when the
communication port 31 is closed may be expressed by the following
equation:
where C is, as shown in FIG. 8, a displacement-pressure ratio of
the diaphragm 32 (m/Pa), A is an area of the diaphragm 32
(m.sup.2), and Vb is a volume of the back chamber housing 6
(cc).
As seen from the equation (9), the output voltage et of the
pressure sensor 5 when the communication port 31 is closed is
subjected to the influence of a variation in the volume Vb of the
back chamber housing 6. FIG. 9 shows output characteristics of the
pressure sensor 5 when the volume Vb and the static pressure Po
change.
The volume of fuel Vf within the fuel tank 2 based on the output
from the pressure sensor 5 may be expressed by the following
equation: ##EQU1## where Po' is an initially set value of static
pressure. A measurement error Ef caused by the variation in static
pressure Po may be expressed by the following equation:
##EQU2##
The measurement error Ef, when the static pressure Po was
experimentally changed over a range of 55 to 120 kPa, indicated -2
to +4.5 liters (L) according to a change in the volume of fuel Vf
within the fuel tank 2, as shown in FIG. 10, without correcting the
volume of the back chamber housing 6 to an appropriate value.
The measurement error Ef, as can be seen from the equation (11), is
also dependent upon the volume of the back chamber housing 6. If,
in the equation (11), the measurement error Ef dependent upon the
variation in static pressure Po is set C to zero (0), the volume Vb
of the back chamber housing 6 is ##EQU3##
In this embodiment, the volume Vb of the back chamber housing 6 is
set to about 1 cc which is determined using the equation (12)
assuming that Vf=0 and Po=Po'=100 kPa.
Thus, it will be appreciated that it is possible to decrease the
measurement error Ef to approximately zero ignoring the influence
of the above mentioned offset term
(.gamma..multidot.Po.multidot.kt.multidot.Va) in the equation (7)
caused by the variation in the static pressure Po. Accordingly, the
CPU 46 may determine the volume of fuel Vf within the fuel tank 2
according to the following equation:
In operation, the volumetric measuring apparatus 1 is activated
upon starting of the engine. The speaker 4 is then actuated to
produce volume variations raging from -.DELTA.V to +.DELTA.V. The
volumetric measuring assembly 8 selectively opens and closes the
communication port 31 of the opening and closing unit 7 with given
timing. The pressure sensor 5 thus detects a difference in
pressures when the communication port 31 is opened and when it is
closed. The CPU 46 of the volumetric measuring circuitry 13 is
responsive to the outputs from the pressure sensor 5 to determine
the volume of fuel Vf within the fuel tank 2 according to the above
equation (3) or (13). The display 47 then indicates the amount of
fuel remaining in the fuel tank 2.
As will be appreciated from the above explanation, the volumetric
measuring apparatus 1 of the invention changes the pressures in the
reference enclosure 3 and the fuel tank 2 only using the single
speaker 4 without use of any other additional elements such as
pressure transmission pipes or a selector valve employed in a
conventional system, and determines the volume of fuel stored
within the fuel tank 2 based on the outputs from the single
pressure sensor 5. Therefore, it is possible to simplify an
arrangement of the apparatus, thereby achieving a compact and
lightweight structure thereof at economical costs and decreasing
the possibility of malfunction. Additionally, the volumetric
measuring apparatus 1 of the present invention, as seen from the
above discussion, uses Boyle-Charles's law to determine the volume
of gas filling the fuel tank 2. The gas volume determination can be
achieved by providing the leakage hole 29 communicating the
reference enclosure 3 with the fuel tank 2 without finding a ratio
of specific heat of the gas and a static pressure in the fuel tank
2. This permits the volume of gas in the fuel tank 2 to be
determined with high accuracy.
A second embodiment of the volumetric measuring apparatus 1 will be
discussed below.
While the above first embodiment has the communication port 31
establishing communication between the Back chamber housing 6 and
the reference enclosure 3, the second embodiment has the
communication port 3 1 formed to communicate between the back
chamber housing 6 and the fuel tank 2 which is selectively opened
and closed by the opening and closing unit 7. Additionally, the CPU
46 of the volumetric measuring circuitry 13 uses the following
equation instead of the above equation (1) to determine the volume
of gas Vt.
FIG. 11 shows a third embodiment of the volumetric measuring
apparatus 1.
While in the above first embodiment considers the case where even
though the fuel tank 2 is filled with a liquid fuel, the surface of
the liquid fuel is below the reference enclosure 3, the third
embodiment uses techniques of measuring the volume of a liquid fuel
whose surface reaches the reference enclosure 3.
The reference enclosure 3 has a small chamber housing 51 mounted on
an outer bottom wall thereof. The chamber housing 51 communicates
with the reference enclosure 3 through a leakage hole 29 and also
communicates with the fuel tank 2 through an opening 40 which is so
sized as to allow a liquid fuel to enter the chamber housing 51. In
the chamber housing 51, a float 52 is disposed which has a specific
gravity smaller than that of the liquid fuel and which has a rubber
seal or packing 53 mounted on an upper surface for establishing
liquid-fight seal of the leakage hole 29. Specifically, when the
surface of the liquid fuel reaches the reference enclosure 3, the
float 52 is lifted up so that the packing 53 closes the leakage
hole 29, preventing the liquid fuel from entering the reference
enclosure 3.
The reference enclosure 3 also includes an opening 54 for
maintaining static pressures in the reference enclosure 3 and the
fuel tank 2 at a constant level.
FIG. 12 shows a fourth embodiment of the volumetric measuring
apparatus 1.
While the above first and third embodiments have the leakage hole
29 serving to return a liquid fuel back to the fuel tank 2 which is
collected on the bottom of the reference enclosure 3 when a portion
of a liquid fuel stored in the fuel tank 2 evaporates, enters the
reference enclosure 3, and then is condensed, the fourth embodiment
has a capillary means 56 made of, for example, a fiber member such
as spring or cloth which attracts and elevates a liquid fuel
collected on the bottom of the referenced enclosure 3 near a coil
55 (i.e., a heating element) of the speaker 4. The liquid fuel
elevated is evaporated by the heat of the coil 55 and then returned
back to the fuel tank 2 through the opening 54. Thus, during
operation of the volumetric measuring apparatus 1 (i.e., the
speaker 4), the fuel collected on the bottom of the reference
enclosure 3 is constantly discharged to the fuel tank 2.
FIG. 13 shows a fifth embodiment of the volumetric measuring
apparatus 1.
As can be seen in the drawing, the back chamber housing 6 is
shifted directly by lateral movement of the armature 35 of the
solenoid valve to selectively establish the communication between
the pressure sensor 5 and the inside of the reference enclosure 3
so that the piezoelectric element 33 may be subjected to the
pressure in the reference enclosure 3. Attached to an end of the
back chamber housing 6 is a rubber seal or packing 61 for
establishing liquid-tight seal between an inner wall of the
reference enclosure 3 and the back chamber 70 when the back climber
housing 6 is urged against the inner wall of the reference
enclosure 3.
FIGS. 14 to 16 show a sixth embodiment of the volumetric measuring
apparatus 1 which includes a cylindrical passage or throat 62 for
transmitting a pressure variation produced by the speaker 4 to the
fuel tank 2. The throat 62 has a given length L extending downward
from the bottom of the reference enclosure 3, and establishes
communication between the reference enclosure 3 and the fuel tank 2
through the propagation hole 28. The leakage hole 29 is formed in
the diaphragm of the speaker 4.
Thus, the reference enclosure 3 is hermetically sealed except a
portion communicating with the fuel tank 2 through the throat 62.
This prevents, as can be seen from FIG. 14, the surface of the
liquid fuel stored in the fuel tank 2 from entering the reference
enclosure 3 even when it reaches above the bottom of the throat
62.
The length L of the throat 62 may be determined in the following
manner.
A height x of fuel entering the throat 62 is initially determined
using the following equation:
From the balance of static pressure,
where g is an acceleration acting on the fuel, S is a sectional
area of the cylindrical throat 62, h is a height between a given
maximum level of the fuel and the lower end of the cylindrical
throat 62, and .rho. is a specific gravity of the fuel stored in
the fuel tank 2.
Next, the length L of the cylindrical throat 62 is so determined as
to meet the relation of L.gtoreq.x+a+b where a is a change in level
of the fuel caused by a maximum inclination thereof and b is a
change in level of the fuel caused by vibrations of the surface of
the fuel and/or the fuel tank 2.
When the surface of the fuel in the fuel tank 2 lies, as shown in
FIG. 14, above the lower end of the cylindical throat 62, a space
formed beneath the diaphragm of the speaker 4 is enclosed by the
surface of the fuel to form a small cavity, which restricts the
diaphragm from vibrating so that the pressure change Pc within the
reference enclosure 3 detected by the pressure sensor is decreased.
Additionally, when the surface of the fuel which is, as shown in
FIG. 15, lies below the lower end of the cylindrical throat 62,
rises gradually, the pressure change Pc in the reference enclosure
3 experiences a variation, as shown in FIG. 16, according to an
interval D between the surface of the fuel and the lower end of the
cylindrical throat 62.
Accordingly, when the pressure change Pc in the reference enclosure
3 detected by the pressure sensor 5, as shown in FIG. 16, becomes
smaller than a threshold value P1, the volumetric measuring
circuitry 13 of this embodiment concludes that the surface of the
fuel in the fuel tank 2 is above the lower end of the cylindrical
throat 62, and informs a vehicle operator through the display 47
that the fuel tank 2 is filled up.
As will be discussed below in detail, according to the design of
the cylindrical throat, a variation in the pressure change Pc shown
by the solid line in FIG. 16 may experiences a variation shown by a
broken line so that the pressure change Pc does not become smaller
than the threshold value P1 if the fuel tank 2 is filled up. It is,
thus, difficult to determine with high accuracy whether the fuel
tank is filled up or not. This is due to the resonance phenomena of
a vibration system which generates a vibration of a frequency,
determined by a mass (m) of the fuel entering the cylindrical
throat 62 up to the height x, an air spring constant (ksr) of the
propagation hole 28 (i.e., a confined space defined by the surface
of the fuel within the cylindrical throat 62 and the diaphragm of
the speaker 4), and a mechanical spring constant (ksp) of the
diaphragm of the speaker 4, set near an operating frequency of the
speaker 4. Thus it is advisable that the vibration system be
designed not to resonate at the operating frequency of the speaker
4. The resonance frequency .omega. of the vibration system may be
given by the following relation according to an equation of motion.
##EQU4##
It will thus be appreciated that the resonance frequency .omega. of
the vibration system is expressed as a function of the mass (m) of
the fuel entering the cylindrical throat 62 at the height x, the
air spring constant (ksr) of the propagation hole 28, and the
mechanical spring constant (ksp) of the diaphragm of the speaker 4.
Therefore, the detection of the volume of fuel with which the fuel
tank 2 is filled is accomplished by setting those parameters to
appropriate values, respectively, to eliminate the resonance
phenomena of the vibration system.
FIGS. 18 and 19 show a seventh embodiment of the volumetric
measuring apparatus 1. FIG. 18 is a cross sectional view
illustrating a structure of the volumetric measuring apparatus 1.
FIG. 19 is a traverse sectional view taken along the line I--I in
FIG. 18.
The volumetric measuring apparatus 1 of this embodiment is
different from those in the above embodiments in that the speaker 4
and the volumetric measuring assembly 8 are both disposed on the
bottom of the reference enclosure 3, and the control unit 14 and
the reference enclosure 3 are designed as a unit.
As shown in FIG. 18, a main flange 94 and a metallic flange 95 are
attached to each other through a gasket 92 by fastening bolts 26
into nuts or retainers 90 secured on an upper surface of the fuel
tank 2. A circuit cover 96 of the control unit 14 is mounted or
welded on the metallic flange 95 to define a control unit chamber
100. The main flange 94 isolates the control unit chamber 100 from
art internal space of the reference enclosure 3. The metallic
flange 95 serves as a heat sink of power elements 104, as will be
described later.
On the bottom of the reference enclosure 3, the speaker 4 and the
volumetric measuring assembly 8 are arranged in series. Within the
control unit chamber 100, a circuit board 102 and the power
elements 104 are disposed. The power elements 104 constitute the
speaker driver 11 for operating the speaker 4. The circuit board
102 has mounted thereon various electric parts 108 and an
integrated circuit 110 which form the opening and closing unit
controller 12 and the volumetric measuring circuitry 13.
On the main flange 94, terminals 106 are mounted which electrically
connect the reference enclosure 3 with the control unit 14. Through
the terminals 106 and lead wires 15, the speaker 4 and the
volumetric measuring assembly 8 are connected to the power elements
104 and the circuit board 102, respectively.
As can be seen in the drawings, an arrangement of the speaker 4 and
the volumetric measuring assembly 8 on the bottom of the reference
enclosure 3 decreases a vertical length of the reference enclosure
3 disposed within the fuel tank 2 to achieve a wide range of volume
detection within the fuel tank 2. Additionally, this arrangement
offers easier assembly of the volumetric measuring assembly 8 than
in the above embodiments wherein it is mounted on a side wall of
the reference enclosure 3.
Further, a close arrangement of the circuit board 102 to the main
flange 92 forming an upper wall of the reference enclosure 3
eliminates the influence of noise components appearing on signal
transmission lines extending from the volumetric measuring assembly
8 for accurate detection of the volumetric of fuel stored within
the fuel tank 2.
Referring to FIG. 20, there is shown a modified form of the opening
and closing unit 7 of the volumetric measuring assembly 8 according
to an eighth embodiment.
The opening and closing unit 7 of the this embodiment is different
from that of the first embodiment shown in FIG. 4 in that one end
portion of the armature 35 is formed with a small-diameter
extension whose end is tapered to form a cone 116 and a side wall
114 of a housing has a conical portion 118 bulging outwardly so as
to be contoured to the cone 116.
In the first embodiment as mentioned above, when the solenoid 34 is
energized by the opening and closing unit controller 12, it will
cause the armature 35 to be urged by a magnetic force produced
against the spring force of the spring 36, thereby bringing the end
112 of the armature 35 into engagement with the side wall 114 to
open the communication port 35 so that an uncomfortable mechanical
noise is generated.
In this embodiment, when the solenoid 34 is energized to open the
communication port 35, the tapered surface of the cone 116 of the
armature 35 collides with an inner tapered wall of the conical
portion 118 so that the impact is reduced. An attraction acting on
the armature 35 produced by the solenoid 34 is, as shown in FIG.
21, commonly reduced as the armature approaches the side wall 114.
An attraction produced by this embodiment becomes smaller than that
of the first embodiment immediately before the armature 35 collides
with the side wall 114, so that the mechanical noise is
decreased.
Additionally, the decrease in mechanical noise is also achieved
with circuit design. Specifically, by arranging a capacitor between
the switch operable according to a command from the CPU 46 and
opening and closing unit 7, the rise of voltage upon actuation of
the switch 48 is moderated, thereby reducing the mechanical noise
upon collision of the armature 35 with the side wall 114.
FIG. 22 shows a modified form of the control unit 14 according to a
ninth embodiment which is designed to operate the speaker 4 using
an output signal from the CPU 46 without use of the oscillator 46,
as employed in the first embodiment, for producing a high-accuracy
oscillation frequency, and to give a function of the phase detector
45 to the CPU 46 for realizing a low-priced circuit
arrangement.
The CPU 46 of this embodiment provides a given wave signal to a
band-pass filter 122. The band-pass filter 122 removes therefrom
high-frequency components, and provides it to the power amplifier
42. The power amplifier 42 amplifies the high-frequency removed
signal and produces it to the speaker 4. Additionally, a signal
outputted from the pressure sensor 5 is amplified by the
preamplifier 43 and then sent to the band-pass filter 44 to remove
a noise frequency other than the frequency produced by the CPU 46.
The noise-removed signal is then inputted to the CPU 46 through a
gain-switching amplifier 120 for determination of the volumes of
gas and fuel within the fuel tank 2. Note that the opening and
closing unit 12 is the same as in the first embodiment.
It is commonly possible that a wave signal provided for operating a
speaker is translated into a pulse signal having a given duty cycle
by .delta.-.SIGMA. modulating a sine wave, for example. The CPU 46
of this embodiment produces such a pulse signal directly based on
clocks generated therein.
Further, the CPU 46, as mentioned above, a function of the phase
detector 45 employed in the first embodiment which will be
described below.
FIG. 23 is a circuit block diagram of a phase detector 45
incorporated in the CPU 46. FIGS. 24(a) to (d) illustrate an
operation of the phase detector 45.
The phase detector 45 includes a frequency converter 124 and a
low-pass filter 126. To the frequency converter 124, a signal A
outputted from the pressure sensor 5 through the gain-switching
amplifier 120 and a reference signal B synchronized with an
operating frequency of the speaker 4 are inputted. An output signal
C from the frequency converter 124 is inputted to the low-pass
filter 126.
In operation of the phase detector 45, the frequency converter 124
first multiplies the signal A, as shown in FIG. 24(a), 15 and the
reference signal B, as shown in FIG. 24(b), together to produce a
frequency-converted DC signal C, as shown in FIG. 24(c). This DC
signal then passes through the low-pass filter 126 to produce a
signal D, as shown in FIG. 24(d), which is used in determining the
volume of fuel within the fuel tank 2. An operating wave signal for
the speaker 4 may be provided to the band-pass filter 122 through,
for example, an A/D converter build in the CPU 46 in addition to a
pulse signal, as described above, generated based on clocks in the
CPU 46.
A maximum ratio of an output of the pressure sensor 5 when the
communication port 31 is opened by the opening and closing unit 7
to that when the communication port 31 is closed, reaches as high
as 1000: 1. Thus, amplifying both output signals of the pressure
sensor 5 with the same gain requires that a considerably wide
dynamic range is given to the CPU 46 receiving the amplified output
signals. In this embodiment, however, the use of the gain-switching
amplifier 120 allows the CPU 46 to have a decreased dynamic range.
Accordingly, it becomes possible to achieve high-accuracy
volumetric measurements through an A/D converter having a small
number of bits.
Additionally, the use of a unified structure composed of the
preamplifier 43, the bad-pass filter 44, and the gain-switching
amplifier 120 eliminates the influence of deterioration of the
preamplifier 43 and the band-pass filter 44 as a result of age,
temperature variation, or design error, acting on calculation in
the CPU 46 of a ratio of outputs of the pressure sensor 5 derived
when the communication port 35 is opened and when it is closed to
determine the volume of fuel stored within the fuel tank 2.
While the present invention has been disclosed in terms of the
preferred embodiment in order to facilitate a better understanding
thereof, it should be appreciated that the invention can be
embodied in various ways without departing from the principle of
the invention. Therefore, the invention should be understood to
include all possible embodiments and modification to the shown
embodiments which can be embodied without departing from the
principle of the invention as set forth in the appended claims. For
example, in addition to measurement of the volume of gas in the
fuel tank 2 to determine the volume of the fuel stored therein, it
is possible to measure the volume of gas filling, for example, a
conventional vessel or a room as long as it is substantially
hermetically sealed.
Additionally, the speaker 4 serving as a volume changing means may
alternatively be installed, as shown in FIG. 17, outside the
reference enclosure 3 to produce a pressure variation within the
reference enclosure 3.
Further, while in the above embodiments, the reference enclosure 3
is installed on the inner upper end of the fuel tank 2, it is
possible to arrange it at another location, for example, a side
wall of the fuel tank 2 where the volume of gas in the fuel tank 2
can be measured.
Moreover, the speaker 4 may alternatively be placed with another
suitable volume changing means including, for example, a cylinder
communicating with the reference enclosure 3 and the fuel tank 2
and a piston so arranged as to reciprocate within the cylinder.
* * * * *